Separation of aqueous salt solution by pervaporation through hybrid organic-inorganic membrane: effect of operating conditions

Hybrid polymer-inorganic membranes were prepared by crosslinking poly(vinyl alcohol) (PVA), maleic acid (MA) and silica via an aqueous sol–gel route. Membrane characterisation results revealed silica nanoparticles (b10 nm) were well dispersed in the polymer matrix and significantly reduced swelling of the membrane. The membranes were tested for pervaporation separation of aqueous salt solution with NaCl concentrations of 0.2–5.0 wt% at temperatures 20–65 °C, feed flowrates 30–150 mL/min and permeate pressures 2–40 Torr. The salt rejection remained high (up to 99.9%) under all operating conditions. A high water flux of 11.7 kg/m2 h could be achieved at a feed temperature of 65 °C and a vacuum of 6 Torr. The effect of operating conditions on water flux is discussed in relation to diffusion coefficients of water and fundamental transport mechanism through the membrane. The activation energy for water permeation was found to vary from 23.8 to 20.1 kJ/kmol when the salt concentration in the feed was increased from 0.2 to 5.0 wt%

Ethanol-water separation by pervaporation

The separation of ethanol-water mixtures is of great importance for the production of ethanol from biomass. Both ultrafiltration and pervaporation processes can be used for the continuous processing of fermentation and separation, The removal of ethanol from the ultrafiltration permeate can be accomplished by pervaporation. Separation of ethanol-water mixtures by the pervaporation process has been investigated. Results are presented for membranes which are preferentially permeable for ethanol and for others which are preferentially water permeable. Details on the preparation of several membrane types (homogeneous, asymmetric and composite) are given. A schematic process diagram is given in which the fermentation of sugars to ethanol is membrane-controlled

A rationale for the preparation of asymmetric pervaporation membranes

Pervaporation is carried out primarily with homogeneous membranes. An improvement in permeation rate can be achieved by using asymmetric or composite membranes. In order to maintain a high selectivity, very dense top layers are needed. The formation of asymmetric pervaporation membranes will be discussed in terms of the model proposed by our group: formation of the top layer by gelation; formation of the porous sublayer by liquid-liquid phase separation followed by gelation of the concentrated polymer phase. To obtain very dense top layers the following factors are important: the ratio of nonsolvent inflow and solvent outflow, polymer concentration, location of the liquid-liquid demixing gap, and location of the gel region. Asymmetric membranes have been prepared by varying these factors, and the obtained membranes have been tested on ethanol/water mixtures

Production and Characterization of Zeolite Membrane

The use of bioethanol as an alternative fuel with a purity of more than 99.5% wt has prompted research on bioethanol purification. One of the promising methods used for bioethanol purification is pervaporation membrane. This research is aimed to prepare and characterize zeolite membranes for pervaporation membrane. The membrane preparation consisted of two stages, namely support preparation and zeolite deposition on the support. In support preparation, α alumina and kaolin with spesific composition (50:30; 40:40; 50:30) was mixed with additives and water. After pugging and aging process, the mixture became paste and extruded into tubular shape. The tube was then calcined at temperature of 1250 °C for 3 hours. After that, zeolite 4A is deposited on the tubes using clear solution made of 10 %wt zeolite and 90 %wt water and heated at temperature of 80 °C for 3 hours. Furthermore, the resulting zeolite membranes was washed with deionized water for 5 minutes and dried in oven at temperature of 100 °C for 24 hours. Characterization of zeolite membranes included mechanical strength test, XRD, and SEM. In the mechanical strength test, the membrane sample with alumina:kaolin = 50:30 (#membrane A#) has the highest mechanical strength of 46.65 N/mm2. Result of XRD analysis for the membran A indicated that mullite and corundum phases were formed, which mullite phase was more dominant. Meanwhile the result of SEM analysis shows that zeolite crystals have been formed and covered the pores support, but the deposition of zeolite has not been optimal yet. The performance examination for bioethanol purification showed that the membrane could increase the purty of bioethanol from 95% to 98% wt

Terminology for Membrane Distillation

One of the subjects of the “Round Table ” at the “Workshop on Membrane Distillation ” in Rome on May 5,1986 was nomenclature. The best example for the need of a more uniform language is the name of the process itself. In Rome the following names were used by the authors present: membrane distillation

Green synthesis of vanillin: Pervaporation and dialysis for process intensification in a membrane reactor

In the present work, two different membrane processes (pervaporation and dialysis) are compared in view of their utilization in a membrane reactor, where vanillin, which is probably the most important aroma of the food industry, is synthesized in a green and sustainable way. The utilized precursor (ferulic acid, which is possibly a natural product from agricultural wastes) is partially oxidized (photocatalytically or biologically) and the product is continuously recovered from the reacting solution by the membrane process to avoid its degradation. It is observed that pervaporation is much more selective towards vanillin than dialysis, but the permeate flux of dialysis is much higher. Furthermore, dialysis can work also at lower temperatures and can be used to continuously restore the consumed substrate into the reacting mixture. A mathematical model of the integrated process (reaction combined with membrane separation) reproduces quite satisfactorily the experimental results and can be used for the analysis and the design of the process

Organo-Silica Membrane Prepared from TEOS-TEVS Modified with Organic-Acid Catalyst for Brackish Water Desalination

The sol gel process is one of the processes used in the manufacture of thin films on membranes because it can control the pore size in the resulting silica matrix. In addition, another way to build membrane size can be done by adding catalysts and precursors to be used. In this study, using a combination of tetraethyl ortho silicate (TEOS) and triethoxy vinyl silane (TEVS) precursors and citric acid as a catalyst to produce a silica matrix with mesoporous size so that it is suitable for application in the desalination process. The organo silica membrane was calcined at 350 ° C for 1 hour using the RTP calcination technique under vacuum, thus preventing the decomposition of carbon in the silica matrix. The membrane was dipcoated 4 times to obtain 4 layers. The FTIR (Fourier-transform Infrared Spectroscopy) test was carried out to see the functional groups on xerogel, namely silanol, siloxane and carbon. In addition, the performance of this membrane is carried out by desalination through pervaporation using 0.3% NaCl feed water with variations in feed air temperature, namely 25 ℃, 40 ℃ and 60 ℃. The resulting flux of air value increased with increasing feed water temperature, namely 6.1; 11.2; and 12.1 kg.m-2h-1 while the resulting salt rejection was 99.72; 99.64 and 99.23%. So that the organo silica membrane is suitable when applied to the desalination process through pervaporation. 

Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 m have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent

Enhanced membrane distillation : analytical and deionization applications

Membrane distillation (MD) is a newer technology that is being investigated for applications such as seawater desalination and concentration of fruit and sucrose solutions. The major advantage of MD over traditional thermal distillation is that it requires a substantially lower thermal energy requirement to power the process. This allows low grade energy sources such as waste heat or solar energy to be used with MD. Compared to concentration processes such as reversed osmosis or ion-exchange, MD does not require specialized equipment, high electrical consumption, the use of strong acids and bases nor does it generate hazardous waste as a by-product. In membrane distillation, a heated solution is passed through the lumen of a hollow fiber porous hydrophobic membrane. The vapor pressure differential between the cool and hot side of the membrane allows the vapor to pass across the pores but prevents passage of the liquid phase. Unlike pervaporation, which also relies on differential vapor pressure, MD also involves the transfer of a significant amount of heat across the membrane. MD processes to date have demonstrated several inefficiencies that cause it to be a relatively low yield process. These inefficiencies include conductive heat loss through the membrane material, temperature polarization at the bulk feed-membrane interface, pore wetting and effective use of available membrane surface area. In this investigation, traditional membrane distillation was compared to membrane distillation using the same starting membrane material but which had carbon nanotubes (CNTs) incorporated into the membrane pores. The modified membrane is referred to as carbon nanotube immobilized membrane (CNIM). It was demonstrated that several properties of CNTs aided in improving the performance of MD. These include high thermal conductance, rapid sorption-desorption ability, ability to transport water in a rapid ordered manner and hydrophobic characteristics. Experiments were conducted where MD was used as a preconcentration technique to analyze trace quantities of drug substance in water. CNIM provided much higher levels of enrichment for the analytes of interest than did preconcentration using the plain membrane. Another set of experiments was then successfully conducted that demonstrated that CNIM-MD was applicable to the preconcentration of drug products in a polar solvent. Desalination experiments were completed that showed that CNIM provided significantly higher levels of salt reduction and flux at a lower energy requirement than did the standard membrane. Finally, MD-CNIM was investigated as a means to remove or concentrate trace levels of inorganic impurities from an aqueous matrix. Overall, it was demonstrated that MD using CNIM provided a more efficient process with significantly higher solvent reduction and levels of enrichment than did MD using plain membranes

Microemulsion breakdown by pervaporation technique: Effect of the alkyl chain length of n-alkanol, a cosurfactant of the microemulsion

Two sets of microemulsions, cyclohexane- and water-rich ones, were prepared with the following n-alkanols as cosurfactants: n-propanol, n-butanol, n-pentanol, and n-hexanol. The results showed the influence of the alkyl chain length of the n-alkanol on the permselectivity properties of the pervaporation technique in the breakdown of the microemulsions. The variations of the total flux rate J and the enrichment factor β were in parallel with the effect of the cosurfactant on the swelling extent of the PDMS membrane